Stereo transducer



Dea -24, 1963 H. J. SMlTS STEREO TRANSDUCER Filed Dec. 31, 1959 INVENTOR 'H.J. SMITS AGENT United States Patent 3,115,554 STEREO TRANSDUCER Hubcrtus Jan Smits, Eindhoven, Netherlands, assignor to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware Filed Dec. 31, 1959, Scr. No. 863,174 Claims priority, application Netherlands .l'an. 2, 1959 3 Claims. (Cl. 179-100.41)

The invention relates to a transducing device for recording or scanning a phonograph record disc, in which two signals of different oscillation directions are simultaneously recorded with the aid of a common recording or scanning member which is in mechanical contact with two relatively independently operative transducing elements through a coupling piece, in which the composition or the separation into double information takes place.

The transducing device according to the invention is characterized in that the coupling piece, on each side of the needle holder which is in mechanical contact with the coupling piece, consists of at least two materials, the clasticity moduli of these materials differing to such an extent that the parts of each branch made from these materialsirrespective of their dimensionsexhibit a relative difference in rigidity.

The present invention has for its object the provision of a transducing device in which the transmission path between the needle holder and the transducing elements is characterized by a very slack i.e. compliant, deformable, supple, yieldable, under compression coupling, so that the needle point is able to follow the modulations in the grooves of the record with the required accuracy. This separation of the double information is at a maximum and in the case of strong modulations, the needle does not whip out of the groove; otherwise a greater needle force would be required which would entail greater wear of the needle and/ or the record. Furthermore, a smaller needle force will sufiice, which the modern development of record player designs tends to achieve.

With the groove scanners of the known kind the coupling piece is subjected to an initial tensile stress and is formed so that at the area of contact between the coupling piece and the needle holder forms an angle of less than 180. Thus the coupling piece, situated between the needle holder and the following hinged point, is, when the needle point is excited by the modulations in the grooves, under strain of tensile force, so that the rigidity of the coupling piece may be considerably reduced.

However, if the two branches of the coupling piece subjected to tensile force are each made from only very slack material (in principle the material parts of the coupling piece on either side of the point of contact between the needle holder and the coupling piece may even be replaced by cords) it appears that losses occur in the transmission of the mechanical energy to the transducing elements, which results not only in a general attenuation of the signal but mostly in a reduction of the high tones. Therefore, to overcome this defect, the coupling piece, according to this invention, is modified so that each branch of the coupling piece consists of at least two materials, of which the elasticity moduli differ so that the parts of each branch made from these materialsirrespective of their dimensionsexhibit a relative difference in rigidity. It will be understood, with the following further explanation that those combinations of materials in the same branch, which, although belonging to the same class of materialsfor example the class of the polyvinyl chloridescannot be considered to be the same materials, since they have a different elasticity modulus, for example by adding a different percentage of softener; this is described inter alia in the review Kunststotfe,

Patented Dec. 24, 1963 41, 1951, Number 3, pages 89-97. A suitable material is, in general, any material having adequate internal damping, since otherwise resonance phenomena would occur, which might disturb the signal transmission and hence the frequency characteristics in the reproduction.

The structure according to the present invention is preferably used with rotating transducing elements, since it is thus possible, inter alia by suitable journalling, to use only small forces, so that the coupling piece may be as small and elastic as possible. As soon as this principle is applied to crystal elements, the coupling piece must be larger and yieldable to capture the needle motions, since the clamping of the rigid crystal, which is to be stressed, increases the rigidity of the assembly.

In a particular embodiment of the transducing device constructed in accordance with the present invention the materials in each branch of the coupling piece are chosen so that the two branches have substantially the same properties. This is particularly important, if the transducing device is intended for the recording of two stereophonically associated signals or scanning of a grooveshaped stereophonic track. However, if in one case, a monaural signal is to be recorded or scanned with, for example an echo signal or in another case, a double information composed of the said signals in a groove, it may even be desirable for the two branches to have unequal properties.

The rigidity of the transmission path between the needle holder and the transducing elements may be further reduced in accordance with the invention by connecting the branch parts of the coupling piece, on either side of the point of contact between the needle holder and the coupling piece, in the angle formed by the branch parts, so that the branch parts are pre-tensioned by a force equal to the force between the record and the needle.

In accordance with the invention the transducing devices may be constructed so that, if each of the two branches is composed of two kinds of materials, each transducing element is connected to that portion of the branch concerned which is made from the material of the greater rigidity. The portion of the branch with the greater rigidity is preferably made from metal or a synthetic substance and the portion of the branch with the least rigidity is constituted of rubber or a synthetic substance.

The invention will be described more fully with reference to the presently preferred embodiments shown in the figure of the accompanying drawing.

Referring more particularly to the drawing in which is illustrated a magneto-dynamic transducing device for recording or scanning a groove-shaped track in which two signals of different oscillation directions are recorded with the aid of a common recording or scanning member 1, which is in mechanical contact with two relatively independently operative transducing elements or armatures 3 and 4 through a coupling piece 2. These transducing armatures constitute a permanent magnet which is rotatable about its axis and which is included in a magnetic circuit 5 and 6 respectively.

The coupling piece 2 forms an angle of less than in which angle is located the needle holder 7, and consists, on both sides from this location, of two branches 2a and 2b of material having adequate internal damping. The elasticity moduli of these materials 20 and 2b in each branch are independent of the dimensions of the parts made therefrom and are chosen so that in each branch these parts exhibit a great relative diiference in rigidity. The part 2a may, for example, be made of a comparatively slacker material, for example, rubber or a synthetic substance, for instance a polyvinyl chloride (60/40) and the part 2b of a comparatively more rigid material, for example, a metal or a synthetic substance, for instance also a polyvinylchloride (100/0), wherein the number before the slanting line indicates the per centage of polyvinyl chloride and the number after this line the percentage of softener. In the preferred embodiment shown in the figure the parts 2a of each branch are made from a single piece of material; these parts are at an angle of less than 180 to each other, inside which is located the needle holder 7. Each of the magnets or armatures 3 and 4 is connected with the part 2b of the associated branch made from the material of greater rigidity.

What is claimed is:

1. In a stereo transducer for phonograph records the combination comprising a pair of transducing elements, a member for scanning a phonograph record and coupling means comprising a pair of branches for connecting said scanning member With each said transducing element, said means including an inverted generally V-shaped portion consisting of elastic material, the legs of said V-shaped portion being substantially rigid under tension and comparatively non-rigid under compression, said scanning member being connected to said elastic portion at the apex of said V, and a pair of rigid portions, each one of said rigid portions rigidly interconnecting a transducing element with a free end of said elastic portion.

2. A stereo transducer for phonograph records comprising a pair of magnetic circuit members defining air gaps, a pair of rotatable armature members rotatable in said gaps, a scanning member for scanning a record and coupling means comprising a pair of branches for operatively connecting said scanning member with each said armature, said coupling means including a portion of generally inverted V shape consisting of elastic material,

the legs of said V-shaped portion being substantially rigid under tension and comparatively non-rigid under compression, said scanning member being secured to said elastic portion at the apex of said J, and a pair of rigid portions separately interconnecting each free end of a leg of the elastic portion with one of said pair of armature members.

3. A transducer for phonograph records comprising a pair of magnetic circuit members defining air gaps, a pair of rotatable armature members rotatable Within said air gaps, a scanning member for scanning a record and coupling means for operatively connecting said scanning member with each said armature, said coupling means including a portion of generally inverted V shaped configuration consisting of rubber, the legs of said V-shaped portion being substantially rigid under tension and comparatively non-rigid under compression, and a pair of rigid metal branch portions each interconnected one of said armature members with a leg of said inverted V-shaped portion, said scanning member being connected to said inverted V-shaped portion at the apex of said V and being urged against said inverted V-shaped portion by a force substantially equal to the force between said scanning member and the phonograph record.

References Cited in the file of this patent UNITED STATES PATENTS 

1. IN A STEREO TRANSDUCER FOR PHONOGRAPH RECORDS THE COMBINATION COMPRISING A PAIR OF TRANSDUCING ELEMENTS, A MEMBER FOR SCANNING A PHONOGRAPH RECORD AND COUPLING MEANS COMPRISING A PAIR OF BRANCHES FOR CONNECTING SAID SCANNING MEMBER WITH EACH SAID TRANSDUCING ELEMENT, SAID MEANS INCLUDING AN INVERTED GENERALLY V-SHAPED PORTION CONSISTING OF ELASTIC MATERIAL, THE LEGS OF SAID V-SHAPED PORTION BEING SUBSTANTIALLY RIGID UNDER TENSION AND COMPARATIVELY NON-RIGID UNDER COMPRESSION, SAID SCANNING MEMBER BEING CONNECTED TO SAID ELASTIC PORTION AT THE APEX OF SAID V, AND A PAIR OF RIGID PORTIONS, EACH ONE OF SAID RIGID PORTIONS RIGIDLY INTERCONNECTING A TRANSDUCING ELEMENT WITH A FREE END OF SAID ELASTIC PORTION. 